rustdoc: Add some basic Safety sections to unsafe functions (#31639)

components/allocator/lib.rs

@@ -16,6 +16,10 @@ mod platform {
     pub use jemallocator::Jemalloc as Allocator;
 
     /// Get the size of a heap block.
+    ///
+    /// # Safety
+    ///
+    /// Passing a non-heap allocated pointer to this function results in undefined behavior.
     pub unsafe extern "C" fn usable_size(ptr: *const c_void) -> usize {
         jemallocator::usable_size(ptr)
     }
@@ -35,6 +39,10 @@ mod platform {
     use std::os::raw::c_void;
 
     /// Get the size of a heap block.
+    ///
+    /// # Safety
+    ///
+    /// Passing a non-heap allocated pointer to this function results in undefined behavior.
     pub unsafe extern "C" fn usable_size(ptr: *const c_void) -> usize {
         #[cfg(target_vendor = "apple")]
         return libc::malloc_size(ptr);
@@ -56,6 +64,10 @@ mod platform {
     use winapi::um::heapapi::{GetProcessHeap, HeapSize, HeapValidate};
 
     /// Get the size of a heap block.
+    ///
+    /// # Safety
+    ///
+    /// Passing a non-heap allocated pointer to this function results in undefined behavior.
     pub unsafe extern "C" fn usable_size(mut ptr: *const c_void) -> usize {
         let heap = GetProcessHeap();
 

components/gfx/text/shaping/harfbuzz.rs

@@ -47,6 +47,11 @@ pub struct ShapedGlyphEntry {
 }
 
 impl ShapedGlyphData {
+    /// Create a new [`SharedGlyphData`] from the given HarfBuzz buffer.
+    ///
+    /// # Safety
+    ///
+    /// Passing an invalid buffer pointer to this function results in undefined behavior.
     pub unsafe fn new(buffer: *mut hb_buffer_t) -> ShapedGlyphData {
         let mut glyph_count = 0;
         let glyph_infos = hb_buffer_get_glyph_infos(buffer, &mut glyph_count);

components/shared/canvas/webgl.rs

@@ -546,6 +546,11 @@ macro_rules! define_resource_id {
         impl $name {
             #[allow(unsafe_code)]
             #[inline]
+            /// Create a new $name.
+            ///
+            /// # Safety
+            ///
+            /// Using an invalid OpenGL id may result in undefined behavior.
             pub unsafe fn new(id: $type) -> Self {
                 $name(<nonzero_type!($type)>::new_unchecked(id))
             }